Mobile social networks (MSNs) provide users with potential indirect relationships such as friends of friends and similar transitive relationships. However, adversaries may be involved in potential relationships, the trustworthiness of the relationships must be ensured. Thus, the disclosure of private information must be well controlled, and users have to be authenticated. In this paper, we propose a revocable authenticated key agreement system (RAKA), which does not require intensive computation for authentication in MSNs. RAKA not only provides a simple rekeying process but also aggregates multiple successive private key update operations into a single rekeying process. The proposed revocation method incurs low communication overhead on mobile devices using a single message broadcast. RAKA is proved to be resilient against malicious attacks.